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Mechanical ventilation sharath

3.
Mechanical Ventilator
 A mechanical ventilator is a machine that
generates a controlled flow of gas into the patient’s
airway, to support the ventilatory function of the
respiratory system and improves oxygenation,
through application of high oxygen content and a
positive pressure.

4.
Classification
 Robert Chatburn:
 Negative Pressure Ventilators.
 Positive Pressure Ventilators.
 (according to the manner in which they support
ventilation)

5.
Negative Pressure Ventilators
 Exert a negative pressure on the external chest
 Decreasing the intrathoracic pressure during inspiration
allows air to flow into the lung, filling its volume
 Physiologically, this type of assisted ventilation is similar to
spontaneous ventilation
 It is used mainly in chronic respiratory failure associated
with neuromascular conditions such as poliomyleitis,
muscular dystrophy, amyotrophic lateral sclerosis, and
mysthenia gravis.

6.
The Iron Lung
 The iron lung, often referred to in the early days as
the "Drinker respirator", was invented by Phillip
Drinker(1894 – 1972) and Louis Agassiz Shaw
Junior, professors of industrial hygiene at
the Harvard School of Public Health .
 The machine was powered by an electric motor with
air pumps from two vacuum cleaners. The air pumps
changed the pressure inside a rectangular, airtight
metal box, pulling air in and out of the lungs

8.
Biphasic cuirass ventilation
 Biphasic cuirass ventilation (BCV) is a method
of ventilation which requires the patient to wear an
upper body shell or cuirass, so named after the body
armour worn by medieval soldiers.
 The ventilation is biphasic because the cuirass is
attached to a pump which actively controls both
the inspiratory and expiratory phases of the
respiratory cycle .

10.
History
 Andreas Vesalius (1555)
 Vesalius is credited with the first description of positive-
pressure ventilation, but it took 400 years to apply his concept
to patient care. The occasion was the polio epidemic of 1955,
when the demand for assisted ventilation outgrew the supply
of negative-pressure tank ventilators (known as iron lungs).
 In Sweden, all medical schools shut down and medical
students worked in 8-hour shifts as human ventilators,
manually inflating the lungs of afflicted patients.
 Invasive ventilation first used at Massachusetts
General Hospital in 1955.
 Thus began the era of positive-pressure mechanical
ventilation (and the era of intensive care medicine).

14.
 Total Inspiratory Time=
Inspiratory time + Inspiratory Pause Time
Inspiratory Time: Time during which Tidal Volume
is delivered.
Inspiratory Pause time: Time during which Gas is
allowed to distribute from Upper to Lower Airways.

15.
 End Expiratory Pressure: Pressure maintained in the
lungs during the Expiratory Phase.
 If allowed to drop to atmospheric pressure: it is
known as ZEEP (Zero End Expiratory Pressure)
 Negative: NEEP ( Not used any more)
 Positive: PEEP ( Used Commonly)
 Mean Airway Pressure: Pressure during one
Respiratory Cycle.

16.
 Peak Airway Pressure: Maximal Airway Pressure
during any time during Inflation.
 Plateau Pressure: Measured when the tidal inflation
volume is held in the lungs after the end of inflation,
preventing the lungs from deflating.
 End expiratory Pressure is set by the presence or
absence of special devices.

18.
Work of Breathing
 Work is performed whenever an applied force causes
displacement of any mass.
 Work = Mean Pressure x Volume Change (Area
under the Pressure-Volume curve)
Work is done by overcoming:
 Compliance of Lung and Thoracic Cage.
 Resistance of airways.
 Frictional Resistance of Tissues
 Inertia.

19.
Important Terms:
 Compliance: “Ease of Distension of Alveoli”
 Compliance = Change in Volume
 Change in Pressure
 Elastance: Ability of the lung parenchyma to return
to its original form after being stretched.
 Elastance = Change in Pressure
 Change in Volume

21.
 Static Compliance: measured when the flow of air
has ceased, as during Breath holding or during
Apnoea.
 Static Compliance= ∆Volume in Litres
∆ Pressure in cm of H20 (kPascals)
 Compliance of lungs: 0.2 litres/cm of H20 (2.0
L/kPa)
 Compliance of Thoracic Wall: 0.2 Litres/cm of H20.

22.
 Therefore, a Volume change of 0.2 litres in the
thorax is obtained by a pressure of 1 cm of H20
exerted against the lungs in conjunction with a
pressure of 1 cm of H20 against the Thoracic wall,
giving a total Thoracic Compliance of 0.1 litre/cm of
H20.
 = 0.2 = 0.1 litre/cm of H20
 1+1

23.
Resistance:
 It is a measure of opposition to flow, which must be
overcome to move a volume of air through the
patient’s conducting airways in a unit of time.
 Flow Rate = Tidal Volume ( L/sec)
 Inspiratory time
 Resistance = P Peak – P Plateau (cmH20/L/sec)
Flow Rate
Normal: 0.6-2.4 cm H2o/L/sec.

24.
 Time Constant: it is a phenomenon, whereby a given
percentage of a passively exhaled breath of air, will
require a constant amount of time, to be exhaled,
regardless of the starting volume. (with constant
lung mechanics)
 Time Constant = Resistance x Compliance

27.
 Power : Mechanical Ventilators are powered either
by electrical energy or potential energy in
compressed air/oxygen.
 Oxygen Blender: Oxygen blenders need an input of
air and oxygen to blend it to deliver the mixture at
the set FiO2.

33.
 A) Patient effort:
 Pressure
 When the patient attempts to inhale, there occurs a
drop in baseline pressure.
 The ventilator senses the drop in pressure.
 Flow:
 The patient’s inspiratory effort causes a decrease in
the baseline flow through the circuit.

34.
 B) Time:
 A timing mechanism decides the changeover, and is
independent of the patient.
 It is used in:
 - Fully controlled ventilation
 - back up safety system in case the patient fails to
trigger inspiration.

35.
b) Inflation Phase:
 These may be pressure, volume or flow.
 The limit may be reached before inspiration ends
and are used as limiting variables.
 The time period between the end of inspiration and
the start of exhalation is the inspiratory pause time.

37.
 Volume Cycling: Inspiratory Phase ends when a pre-
set volume is delivered.
 Pressure Cycling: Inspiratory Phase ends when the
pressure reaches a pre-set value.
 Time Cycling: Cycling occurs when the Pre-set
inspiratory time is completed.

38.
D) Exhalation Phase
 The only function of the ventilator in the exhalation
phase is to allow the lungs to empty.
 Exhaled volumes may be measured by the lungs
during this phase.
 Exhalation can be to:
 - Atmospheric Pressure ( ZEEP)
 - Sub Atmospheric Pressure (NEEP)
 - Above Atmospheric Pressure (PEEP)

39.
Positive End Expiratory Pressure(PEEP)
 PEEP increases the end- expiratory or baseline
airway pressure to a value greater than atmospheric
(0 cm H2o on the ventilatory manometer)
 It is often used to improve the patient’s oxygenation
status, especially in hypoxemia that is refractory to
high level of Fio2.

41.
Indications for PEEP
1)Refractory Hypoxemia caused by intra-pulmonary
shunting.
 Refractory Hypoxemia is defined as hypoxemia that
responds poorly to moderate to high levels of oxygen.
 May be caused by reduction of Functional Residual
Capacity, Atelectasis, or Low V/Q mismatch.

42.
2) Decreased FRC and Lung Compliance.
• A severely decreased FRC and lung compliance can
increase the Alveolar Opening Pressure.
• This increases the work of breathing, and can lead to
fatigue of respiratory muscles.
• PEEP increases the FRC.

44.
 Normally, the alveolar end-expiratory pressure
equilibrates with atmospheric pressure (zero
pressure)
 The average pleural pressure is approximately -5 cm
of H20.
 The alveolar distending pressure is 5 cm of H20.
 This distending pressure is sufficient to maintain a
normal end-expiratory alveolar volume to overcome
the elastic recoil of the alveolar wall.

48.
Auto PEEP
 The Physiological Manifestation of Hyperinflation
from air trapping is called Intrinsic PEEP.
 IN this condition, the end expiratory pressure
remains positive even in the absence of external
PEEP.
 It can occur due to:
 Abnormal respiratory mechanics of the patient.
 Inappropriate ventilatory settings.

51.
 3) Conditional Variables ( Modes of Ventilation)
 This refers to the pattern of interaction between the
patient and the machine.
 Terms:
 Spontaneous Breath: one which is initiated and
terminated by the patient.
 Mandatory Breath: one in which the ventilator
determines the start or end of inspiration
 A mandatory breath which is patient triggered is
called Assisted Breath.

56.
Spontaneous
 Rate and tidal volume are determined by the patient.
 Role of the Ventilator:
1) Provide inspiratory flow to the patient in a timely
manner.
2) Provide flow adequate to fulfill a patient’s
inspiratory demand (tidal volume or inspiratory
flow)
3) Provide adjunctive modes such as PEEP to
complement a patient’s spontaneous breathing
effort.

57.
Controlled Ventilation (CMV):
 Rate and tidal volume is controlled by the machine.
 Can be given as VOLUME CONTROL or PRESSURE
CONTROL.
 Continuous positive airway pressure (CPAP) refers to
the addition of a fixed amount of positive airway
pressure to spontaneous respirations, in the presence
or absence of an endotracheal tube.

58.
Pressure Control Ventilation
 In PCV The pressure- controlled breaths are time
triggered by a preset respiratory rate.
 Once inspiration begins, a pressure plateau is
created and maintained for a preset inspiratory time.
 Pressure-controlled breaths are therefore time
triggered, pressure limited and time cycled.

59.
 In pressure support, the plateau pressure is
maintained as long as the patient maintains a
spontaneous inspiratory flow.
 In pressure control, the pressure plateau is
maintained for a preset inspiratory time.
 PC, is usually indicated for patients with severe
ARDS who require extremely high peak inspiratory
pressures during mechanical ventilation in a volume
cycled mode.
 They have a higher incidence of barotrauma.

60.
Assisted Ventilation
 Rate is controlled by the patient but the tidal volume
is delivered by the machine.
 ASSIST CONTROL VENTILATION: The patient can
breathe at his own rate assisted by the machine but
in addition the machine delivers a minimum set
number of controlled breaths at the rate set on the
machines.

61.
Intermittent Mandatory Ventilation:
 The patient is allowed to breathe spontaneously with
no machine assistance but the machine delivers a
minimum set rate and tidal volume. Breath Stacking
occurs.
 SIMV: Similar to IMV, but breath stacking is
avoided by synchronising the mandatory breath
delivered by the machine to the patient’s inspiratory
effort. i.e. the mandatory breath is triggered by the
patient.

63.
Pressure Support Ventilation
 Pressure Support Ventilation is used to lower the work of
spontaneous breathing and augment a patient’s
spontaneous tidal volume.
 PSV applies a preset pressure plateau to the patient’s
airway for the duration of a spontaneous breath.
 PSV is considered spontaneous because:
1) They are patient triggered.
2) The tidal volume varies with the patient’s inspiratory
flow demand.
3) Inspiration lasts only for as long as the patient actively
inspires.
4) Inspiration is terminated when the patient’s inspiratory
flow demand decreases to a preset minimum value.

64.
 PSV is patient triggered, pressure limited and flow
cycled.
 PS is used in SIMV mode in order to wean the
patient by:
1) Increasing the patient’s spontaneous tidal volume.
2) Decreases the patients spontaneous respiratory
rate.
3) Decreases the work of breathing.

65.
PRESSURE CONTROLLED INVERSE RATIO
VENTILATION
 It is a version of pressure controlled – CMV in which all
breaths are pressure limited and time cycled and the
patient cannot trigger a breath.
 Net effects of inverse I:E ratio are:
1. Increase in Mean airway pressure (MAP) without
increasing peak pressure despite a constant tidal
volume and PEEP.
2. Improved ventilation of alveoli which have longer time
constants for expansion.
3. Build up of intrinsic PEEP, as the tidal volume cannot
be exhaled before the inspiration begins thus avoiding
end expiratory collapse of the alveoli with long time
constants.

68.
Proportional Assist Ventilation (PAV)
 This is a pressure regulated ventilator mode in which
the inspiratory airway pressure with each breath is
titrated by the ventilator in proportion to the
patient’s inspiratory airflow.
 In PAV, there is no target flow, volume or pressure
during mechanical ventilation.
 The pressure used to provide the pressure support is
variable and is in proportion to the patient’s
pulmonary characteristics (elastance and airflow
resistance) and demand (volume or flow)

69.
 Unlike traditional modes, PAV changes with the
patient’s breathing effort.
 Advantage: It can track changes in breathing effort
over time.
 By varying the pressure to augment flow and volume,
a more uniform breathing pattern becomes possible.
 When PAV is used with CPAP, reduction of
inspiratory work occurs and reaches values close to
those in normal subjects.

70.
Neurally Adapted Ventilatory Assistance (NAVA)
 New mode of Mechanical Ventilation that delivers
ventilatory assist in proportion to the electrical
activity of the diaphragm.
 An Oesophageal catheter is inserted to obtain a
diaphragmatic EMG in order to achieve better
patient-ventilator synchrony.

71.
Knowledge based weaning System (KBW)
 Adjustments are made real time to adjust pressure
support ventilation in order to maintain
 respiratory rate,
 tidal volume and
 end tidal CO2 within a predefined range.
 At a minimal level of pressure support, a trial of
spontaneous breathing is analysed and if successful,
a suggestion is made to discontinue ventilation.

72.
Adaptive Support Ventilation (ASV)
 Similar to Mandatory Minute Ventilation
(MMV),where a set proportion of the minute
ventilation is delivered by the machine and the rest is
by the patient.
 It switches automatically from a PCV-like behaviour
to an SIMV-like or PSV like behaviour, according to
the patient’s status.

73.
 ASV always maintains control of ventilation volume
and guarantees:
 A minimum minute ventilation set by the user.
 An effective tidal volume, well above the theoretical
dead space of the patient.
 A minimal breath rate.

75.
 The ventilator uses test breaths to measure the
system compliance, airway resistance, and any
intrinsic PEEP.
 Following determination of these variables, the
ventilator selects and provides the frequency,
inspiratory time, I:E ratio, and high pressure limit
for mandatory and spontaneous breaths.

76.
Airway Pressure Release Ventilation (APRV)
 In this mode, there are two levels of positive airway
pressure applied for set time periods and
spontaneous breathing is possible at both levels.
 Mandatory breaths can be set and occurs when the
pressure increases from the lower to the higher
pressure.
 It can be conceptualized as two levels of CPAP.
 Also called BiPAP.

77.
Airway Pressure Release Ventilation(APRV)
 It is similar to CPAP in that the patient is allowed to
breathe spontaneously without restriction.
 During spontaneous exhalation, the PEEP is
dropped.(released) to a lower level and this action
simulates an effective exhalation manouvre.

79.
BiPAP
 If the patient is breathing spontaneously, the IPAP
and EPAP may be set at 8 cm H20 and 4 cm H2o
respectively.
 Spontaneous/Timed mode: Breaths per min. is set 2-
5 breaths below the patient’s spontaneous rate.
 Timed mode: BPM is set slightly higher than the
patient’s spontaneous rate.

80.
 The spontaneous breaths are triggered, limited,
controlled and cycled by pressure.
 Mandatory breathes are pressure controlled and
pressure limited but time triggered and time cycled.

81.
DuoPAP and APRV
 Two modes of pressure ventilation.
 These modes support spontaneous breathing at two
operator selected levels of positive airway pressure.
 They can combine spontaneous and mandatory
breaths.
 The spontaneous breaths can be pressure supported.
 Cycling between the two levels can be triggered by
time or patient effort.
 The two modes differ in the operator settings
determining the pattern of breaths.

82.
 In DuoPAP, the switchover between the two levels
depends on the set respiratory rate and the time
setting for T(high). The two pressure levels are set by
P(high) and PEEP.
 The baseline pressure is the PEEP pressure.
 In APRV, the switchover is decided by the time
settings T(high) and T(low) and pressure settings by
the P(high) and P(low).
 The Baseline pressure is P(low) pressure.

83.
Pressure Regulated Volume Controlled
 This mode is a form of closed loop ventilation
 Combines features of volume & pressure ventilation
 It is used primarily to achieve volume support while
keeping the peak inspiratory pressure (PIP) at lowest level
possible.
 This is achieved by altering the peak flow and inspiratory
time in response to changing airway or compliance
characteristics.
 First test breath is delivered to calculate compliance

86.
Volume Assured Pressure Support (VAPS)
 Incorporates inspiratory pressure support
ventilation (PSV) with conventional volume-assisted
cycles.
 In VAPS, the therapist must preset the desired
minimum tidal volume and the pressure support
level.
 During VAPS, the mechanical breaths may be patient
or time triggered.
 Once a breath is triggered, the ventilator tries to
reach the pressure support level as soon as possible.

87.
 The delivered volume is then compared with the
preset volume for further action by the ventilator.